The Future of Hydraulic Control in Water-Systems

Transcription

1 The Future of Hydraulic Control in Water-Systems A. Heimann Manager of R&D and of Technical Support & Applications Engineering departments at Dorot Automatic Control Valves Dorot Control Valves, Kibbutz Dorot, Israel Tel: ; Mob: Keywords: PRV, Electronic Control, Pressure Management Abstract Municipal and national water production, treatment and supply systems are complex and have dynamically-changing demand and supply characteristics. However, with the exception of pressure-management controllers, mainly oriented to leakage reduction, most of the hydraulic control of these systems rely on control-valves with, either, constantposition or constant set-value devices- that do not re-adjust dynamically adjust to the changing system s behaviour. Both Hydraulic Pilot-operated, and motorized automatic control valves (ACVs) are widely employed in municipal and national water supply systems, in a variety of applications and control-functions. To generalize and for historic reasons, pilot-operated valve are known and used by most of the engineers and operators as PRVs and PSVs (Pressure Reducing and Pressure Sustaining\Relief Valves), while other control-functions would often be implemented using motorized valves. The aim of this paper is to present a new approach to design and configuration of controllers, which will control pilot-operated valves providing: -A wider range of control-functions -Unlimited combination of control function -Dynamic control of all functions simultaneously -Enable the today s SCADA systems to use the control valve as integral end-point. Control Valves and their Uses in Water-Supply Systems Motorized Valves Motorized gate, butterfly, ball and plunger valves are widely used all over the world for both on\off control functions, such as filling a tank or isolating a sector in certain conditions. In some cases such valves are also used as regulators primarily for flow control. These valves are controlled by an electronic controller, which controls the rotation direction of the electric motor and receive as a feedback the plug position. The plugposition is changed in order to reach the required value of the controlled parameter (e.g. pressure, flow, level etc.) i.e. the controlled parameter is not directly controlled. Actuating the motor consumes electric power, moves the plug at a constant pace (regardless of deviation from set-point), and the number of actuations/minute is limited. Hence, in most cases their position would be fixed for long period and would not act in real-time for any small deviation in the value of the regulated parameter. Each controlfunction must have its own algorithm written for the specific case. In case of power cut-off, the control is lost and the plug will stay in its last position

2 Pilot-Operated Hydraulic Valves As mentioned above, pilot-operated valves are mostly used as PRVs. These valves are controlled by a pilot-valve which is a hydro-mechanical device. The pilot-valve is adjusted by a bias-spring that is compressed to provide a constant regulated value. It reacts in realtime to any change in the controlled parameter, with no external energy consumption. The valve position in this case is the result of the regulation and not the target. The primary reason for using these PRVs is reducing the leakage volume, the rate of ruptures and increasing the overall lifespan of the pipe system. There are many applications where a multi-function control would be required. For example, PSV function is important addition to PRV when there are sensitive customers (hospital, factories ) upstream of the valves. In case of automatic hydraulic valves, the control functions are defined by the type of the pilot-valves and the way they are assembled in the control-loop. With these valves, each pilot-valve would represent a single control-function with a single defined set-value, e.g.: combination of few control-functions would require multiple control devices (pilot-valves, relay-valves and solenoid-valves). Furthermore a pilot-valve, being a hydro-mechanical device, can regulate only parameters that can be mechanically translated to pilot-valve s movements and acting in reference to the bias spring. Other parameters, which cannot be measured that way- such as salinity, turbidity, temperature etc. cannot be controlled by this hydro-mechanical pilot valve. * With the exception of downstream pressure-reduction which has a few options for modulating its set-value by flow, by time and\or by target-point pressure

3 Use of pressure-reducing valves controlled by electronic controllers is a wellknown, widely applied practise. These modulated PRVs provide an improved efficiency and better performance than the simple pilot-operated PRV. The vast majority of the controllers in the market modify the setting of a hydromechanical pilot-valve by manipulating its bias-spring compression force, therefore are limited to the control function of the specific pilot-valve (pressure-reducing), and cannot control any additional parameter. Pilot operated Hydraulically Modulating PRV Pilot operated Electronically Modulating PRV Combined functions Dynamic Control of Hydraulic Parameters Required Control-Functions and the Old Practise to Implement Them In many cases, the efficiency, stability and reliability of the water delivery in the entire network can be improved by controlling other hydraulic parameters than just downstredam pressure. Other control functions may improve efficiency of water-system s operation- such as: Upstream-pressure sustaining Flow rate control Level control Remote on\off control Valve reactions that may reduce or eliminates transient pressures - 3 -

4 Pre-set response of a specific parameter control, to the value of another one in the network. Electronically Controlled Hydraulic Valves Nowadays a new concept is being adopted: control valves that are electronically controlled. These are able to performing: Any required control-function or combination of control functions Reduce OPEX due to standardization of the control-devices regardless of the variety of control functions and simplicity of maintenance. React in real-time with high-sensitivity Low-power, battery-energized No limitation on the ability to modulate each set-value separately Controlling electronically-sensed parameters such as salinity, temperature etc. Wired or wireless remote controlled (SCADA or other). These control systems include four modules: a. Main valve: hydraulically actuated in most cases, but can also be a motorized valve b. A pilot system contains, as control devices, two solenoid-valves, regardless of the complexity of the control-functions and the number of functions controlled by the single main valve. c. A controller that is unique (compared with previous technology) in that it enables the user to configure any control-function and combination of those, without having to have a specific software written per case. It would also be configurable to any control-function by anyone authorized by the user, with no reliance on specialized equipment or programmers. In this case the control of the implementation and the way it is implemented is shifting away from the supplier to the operator\user. The end-user is able to implement highly complex control-functions for specific cases by using stock items and without being limited by availability and expertise. d. Electronic sensors and control inputs which are specific per case (ex.: pressure or level control would require pressure sensors, flow control would require flowsensors, salinity control would require conductivity sensor etc.) This concept allows greater flexibility, compared to older technology as a computer relates to a type-writer (for motor or pilot-valve actuated valves) or to a word-processor if compared to pressure-management controllers that control pilot-valves. Both of the later technologies are mechanical and are limited to specific functions while the presented concept allows way more than just that. Examples Pressure-Management Any of the currently known pressure-reducing functions can be implemented using the EC (Electronically Controlled) valve: fixed set-pressure, time-modulated and\or flowmodulated pressure and closed-loop target-point pressure control (1)

5 The following graph shows a project in the UK where an existing 600 mm motorized valve was replaced with 600 mm electronically controlled Dorot valve. With the motorized valve, downstream pressure, represented by the green line, was oscillating ±4-5m and the flow changes were erratic since the valve position did not change in real time. After commissioning the electronically controlled (EC) Dorot valve, downstream pressure control improved substantially and the flow pattern smoothed. The graph shows a steady flat line at the outlet of the valve, even during the night period when the flow was lower. However much more can be achieved by adding to these functions the following: - Upstream pressure control for PRVs that are located in the boundaries between two adjacent zones. This enables a link between the two zones that will operate to ensure that the critical network is supported. Water is supplied from the adjacent network when required but the valve will never extract more water than the supporting network can supply. This produces a network with a smooth hydraulic profile which reduces customer demand leakage and burst rate and protects adjacent zones from a pressure drop in case a large break or exceptional high demand exist in one. (2) - 5 -

6 Zone 2 Zone 3 Zone 4 Zone 1 Zone 5 - Excessive Flow Shutoff: a safety function that shuts the valve closed in case the flow through it exceeds the maximal set value (an indication to a large rupture in the downstream system). This function, when implemented with a mechanical pilot-system is set for a flow that is the maximal expected flow (at maximal demand) + 25%, but with this new system can have a set-value that is changing according to the normal demand patterns in the zone (eg. be lower during the lowdemand times and higher during high-demand) - The valve can be remotely controlled so to fully open or set to a higher set-value during fire or other exceptional events that require such innervation Controlling Tanks and Reservoirs Controlling the supply of water into tanks and reservoirs is done by opening the valves either by a float that is used to control the valve to fill the tank when the level is low and close it when it is maximal or by manual, local or remote, operations. With the EC control, the upstream pressure can be modulated in order to control the pressure in the network supplying to that reservoir, thus using the same methodologies which are used for pressure-reduction (fixed set-value, time modulated or target-point modulated) to achieve the benefits of pressure-management in the supplying network. Further option would be level-modulated flow control reducing the flow as the level rises, thus avoiding water-hammer \ pressure-surges when the valve closes at the maximal level. Filling hours can be managed so that maximal filling-flow would be during lower-cost supply hours, such as in case of pumped-supply Supplying Flow From various Sources This type of control may have few applications

7 It can be used to batch two water sources that have different qualities, such as different salinity or temperatures, into one with required set-value of mixture. High Salinity Low salinity Allowed\Regulated Salinity Another example is the supply or water from different sources, each has a different cost. (3) The aim in this case would be to supply the maximal flow possible from the lowest cost source, than using the source that is higher than the previous and so on while using the highest-cost source only when lower-cost sources are fully utilized. This can be achieved by either regulating the supply pressure or the flow while considering the demand (via downstream pressure limitation) Source A Lowest cost Source B Intermediate cost Source C High cost Summary Today s technology enables the production of new control devices that provide watersystem designers greater flexibility than ever. This allows the water network to be designed in a way that considers its dynamic behaviour and allocate control-valves in it, that will response to that behaviour, stabilize it and increase its efficiency and reliability. These control valves are no longer limited to perform a fixed set of functions based on mechanical-logic pilot-valves but can perform any control-function or combination of thereof, be remotely controlled and supervised and have flexible algorithm that is software-based. References X.Diaz (2017), Condor and SKYPlatform - Specifications Dorot Valves Publications (2017) ConDor Applications Dorot Valves Publications (2010) S300 Design Manual Controlo 2016 Proceeding of the 12 th Portuguese conf. on automatic control ISBN A. Heimann, (2001), Electronic Control of Pilot-Operated Hydraulic Valves Pipeguild (2014) Entry form for Award for significant contribution to utility pipeline technology Dr. B.Plemper (2012), Case Study: A trial investigating the suitability of globe type valves as primary control valve in a strategic trunk mains system. Dr. B.Plemper & M.Redman, (2010) Asset Management Environmental Innovation conference